Probability Summary

This handout was produced in OpenOffice and converted using the Save As HTML function. I've tidied the HTML up a bit and added the local style sheet. You can download the PDF version for printing. This summary covers the requirements of the new 2010 syllabus we are using up to grade C content. Its tree diagrams for the Grade B 'middle set' level we are teaching to, notes in production...

1.Probability scale

Probabilities can be fractions like
,
decimal fractions like 0.75 or percentages.

“One in two chance” isn't a probability, nor
is 1:6.

2.Trials, events and outcomes

Tossing a coin could be a trial. An event
could be 'coin lands heads side up', and you can estimate the
probability of that event as
.
An outcome is what you observe when the coin lands. Events and
outcomes have to be SMART. 'It rains tomorrow' is not a SMART event
or outcome! How could you make a SMART event about tomorrow's
weather?

3.Probability formula

.

An example would be rolling a dice and getting a
prime number (2, 3, 5)

4.Probability that an event does not happen

An event either happens or it does not. So the
probability of the event happening and the probability of it not
happening have to add to 1. So...

The probability of rolling a square number on a
dice is

The probability of not getting a square number
when you roll a dice is

5.Mutually exclusive events (OR means ADD)

Mutually exclusive events cannot happen at the
same time. If you pick a ball out of a bag, the ball can't be green
and blue, it has to be one colour or the other.